1. Field of the Invention
The present invention relates to a wireless local access network (WLAN), and more particularly, to a procedure in which a station switches a frequency band currently used to another frequency band in a WLAN system.
2. Discussion of the Related Art
With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
Ever since the institute of electrical and electronics engineers (IEEE) 802, i.e., a standardization organization for WLAN technologies, was established in February 1980, many standardization works have been conducted. In the initial WLAN technology, a frequency of 2.4 GHz was used according to the IEEE 802.11 to support a data rate of 1 to 2 Mbps by using frequency hopping, spread spectrum, infrared communication, etc. Recently, the WLAN technology can support a data rate of up to 54 Mbps by using orthogonal frequency division multiplex (OFDM). In addition, the IEEE 802.11 is developing or commercializing standards of various technologies such as quality of service (QoS) improvement, access point protocol compatibility, security enhancement, radio resource measurement, wireless access in vehicular environments, fast roaming, mesh networks, inter-working with external networks, wireless network management, etc.
In the IEEE 802.11, the IEEE 802.11b supports a data transfer rate of up to 11 Mbps by using a frequency band of 2.4 GHz. The IEEE 802.11a commercialized after the IEEE 802.11b uses a frequency band of 5 GHz instead of the frequency band of 2.4 GHz and thus significantly reduces influence of interference in comparison with the very congested frequency band of 2.4 GHz. In addition, the IEEE 802.11a has improved the data transfer rate to up to 54 Mbps by using the OFDM technology. Disadvantageously, however, the IEEE 802.11a has a shorter communication distance than the IEEE 802.11b. Similarly to the IEEE 802.11b, the IEEE 802.11g implements the data transfer rate of up to 54 Mbps by using the frequency band of 2.4 GHz. Due to its backward compatibility, the IEEE 802.11g is drawing attention, and is advantageous over the IEEE 802.11a in terms of the communication distance.
The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data transfer rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to 540 Mbps or higher, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate. In addition, this standard may use a coding scheme which transmits several duplicate copies to increase data reliability and also may use the OFDM to support a higher data rate.
With the widespread use of the WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing rate supported by the IEEE 802.11n. However, an IEEE 802.11n medium access control (MAC)/physical layer (PHY) protocol is not effective to provide a throughput of 1 Gbps or higher. This is because the IEEE 802.11n MAC/PHY protocol is designed for an operation of a single station (STA), that is, an STA having one network interface card (NIC), and thus when a frame throughput is increased while conforming to the conventional IEEE 802.11n MAC/PHY protocol, a resultant additional overhead is also increased. Consequently, there is a limitation in increasing a throughput of a wireless communication network while conforming to the conventional IEEE 802.11n MAC/PHY protocol, that is, a single STA architecture.
Therefore, to achieve a data processing rate of 1 Gbps or higher in the wireless communication system, a new system different from the conventional IEEE 802.11n MAC/PHY protocol (i.e., the single STA architecture) is required. A very high throughput (VHT) WLAN system is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing rate of 1 Gbps or higher in a MAC service access point (SAP). The VHT system is named arbitrarily. To provide a throughput of 1 Gbps or higher, a feasibility test is currently being conducted for the VHT system using 4?4 MIMO and a channel bandwidth of 80 MHz.
A method using a band of 6 GHz or lower and a method using a band of 60 GHz are currently discussed as a method for achieving a throughput of 1 Gbps or higher in a very high throughput (VHT) wireless local access network (WLAN) system. Herein, the throughput of 1 Gbps or higher is used as a criterion, and is a value measured by a medium access control (MAC) service access point (SAP). An access point (AP) supporting a VHT and a non-AP station (STA) may have a MAC/physical layer (PHY) protocol operating in a band of 6 GHz or lower and/or in a band of 60 GHz. An STA that can operate in both the band of 6 GHz or lower and the band of 60 GHz, that is, an STA that supports a VHT protocol in both the band of 6 GHz or lower and the band of 60 GHz is referred to as a multi-band VHT STA.
The band of 6 GHz or lower shows a relatively wide service coverage but disadvantageously has a small available channel bandwidth. On the other hand, the band of 60 GHz advantageously has a great available channel bandwidth, but disadvantageously has a narrower service coverage than the channel using the band of 6 GHz or lower according to a channel property. The two bands may be both used in a method of effectively using the advantages and disadvantages of the two bands. That is, in this method, a multi-band VHT STA is used.
For example, when communication is performed between multi-band VHT STAs located close to each other, a channel using the band of 60 GHz is used, whereas when communication is performed between multi-band VHT STAs located relatively far from each other, a channel using the band of 6 GHz or lower is used. In this manner, when located close to each other, a high throughput can be achieved by using a relatively wide channel bandwidth in the channel using the band of 60 GHz, whereas when located far from each other, reliable communication can be achieved by using the channel using the band of 6 GHz or lower even if a throughput is slightly decreased. In the latter case, instead of the VHT protocol, communication can be performed by utilizing the conventional WLAN protocol, e.g., institute of electrical and electronics engineers (IEEE) 802.11a/b/g/n or the like.
In order for the multi-band VHT STA to communicate in both the band of 60 GHz and the band of 6 GHz or lower in this manner, there is a need to define a band switching procedure. However, such a band switching procedure is not defined in the currently available WLAN technology.